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leetcode [python] 【206】Reverse Linked List

2016-03-30 16:22 711 查看

1 设置两个指针，记录当前结点和上一结点：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
def reverseList(self, head):
"""
:type head: ListNode
:rtype: ListNode

"""
if head == None:
return head
p = head
n = head.next
p.next = None
while n:
t = n.next
n.next = p
p = n
n = t
return p

2 设置一个中间结点，存储每一步结点的上一个结点地址：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
def reverseList(self, head):
"""
:type head: ListNode
:rtype: ListNode

"""
tmp = ListNode(0)
while head:
n = head.next
head.next = tmp.next
tmp.next = head
head = n
return head

如果用递归的方式：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        return self.reverseNode(head, None)
    def  reverseNode(self, head, before):
        if head == None:
            return before
        n = head.next
        head.next = before
        return self.reverseNode(n, head)

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